“Our observations of recall in Old World monkeys suggests that it may have been adaptive in primates for more than 30 million years, and that it does not depend on language or anything else that is uniquely human,” Basile says.

“We believe we have found a new method for testing animals that opens a whole new window into the world of non-human memory research,” Basile adds. “For the first time, monkeys can actually tell us what they recollect, and their test results are directly comparable to human tests.”

Humans have many different forms of memory that can be used in different ways. Recognition, for instance, demonstrates your ability to identify your house when shown a picture of it. Recall shows your ability to draw or describe your house, based solely on your memory of it.

In humans, recognition and recall tests can be supported by two different types of memory. This difference is most clearly seen in some rare cases of amnesia, where patients can easily recognize objects that are before them, but have lost the ability to recall those same objects when they are out of sight.

Previous research has established the ability of monkeys and many other animals to recognize objects. The problem of language, however, has thwarted efforts to test recall in non-humans.

The Emory scientists overcame the language barrier by teaching the rhesus monkeys to “draw.” The monkeys were shown simple shapes on a computer screen. Later, they were presented with a computer touchscreen that allowed them to recreate those shapes by touching the corresponding areas of a grid. The monkeys learned through trial and error that reproducing the shapes they had seen previously would bring a food reward. Once trained, the monkeys were able to transfer their memory skill to novel shapes.

The performance of the monkeys on the computer touchscreen paralleled that of humans using the Rey-Osterrieth Complex Figure Test, a standard human recall test, in which subjects draw a complicated shape from memory.

“Humans certainly recall more complex and sophisticated things over longer time periods,” Basile says. “But we’ve shown that for simple shapes, monkeys have a pattern of performance for recognition and recall that mirrors that of humans. And their ability to immediately transfer their performance to new shapes suggests that we’re tapping into some general cognitive capacity.”

Different types of memory may have evolved to solve a range of problems. Recognizing something as familiar, for instance, is quick and might allow for rapid responses to sightings of food and predators. Recollecting absent information is slower, and might support a more detailed and flexible use of memory, possibly knowledge of distant food locations or past social interactions for planning future behavior.